1. Field of the Invention
The present invention relates to weight lifting exercise devices and, in particular, to a weight lifting exercise device in which the weight resistance experienced by the user may be varied to control the segments of maximum and minimum resistance throughout the exercise movement.
2. Description of the Prior Art
It has been discovered that in developing certain body muscles by weight lifting, it is desirable that those muscles be subjected to a maximum resistance at selected segments in the exercise movement. However, most prior exercise apparatuses do not achieve a variance resistance during the exercise movement and only provide a constant resistance during the exercise. As used herein, "resistance force" will be taken to mean that force which must be overcome by the user in completing the initial one-half of the exercise movement or cycle.
In the field of weight lifting exercise apparatus, the most basic form of apparatus comprises an elongated tubular bar having a predetermined amount of weight in the form of weight members attached to the opposite ends thereof. To exercise with such apparatus, the user grasps the elongated bar and lifts the apparatus throughout a predetermined exercise movement. However, because the only force resisting the exercise movement is gravity which exerts a downward force of constant magnitude, the user experiences a constant resistance throughout the exercise movement.
As is known, the art has addressed the undesirability of requiring the user to manually attach and detach the weight members from the elongated bar by providing a mechanized apparatus which facilitates weight selection. Such an apparatus, referred to herein as a "standard" weight lifting exercise apparatus, typically includes a main support frame having upright members interconnected with crossmembers, a weight support carriage vertically movable within the main frame and having means for detachably supporting weight members; a cable guide means fixed to the main frame; a length of cable secured at one end to the weight support carriage and reeved about the cable guide means; and a gripping means such as a handle which is secured to the free end of the cable which may be grasped by the user to transmit force to vertically move the weight support carriage. It will be appreciated, however, that the resistance experienced by the user is the constant downward force of gravity on the weight support carriage. As such, the resistance is constant throughout the exercise movement and does not vary to achieve the benefits of maximum resistance at selected segments of the exercise movement which are discussed above.
In an alternative embodiment of the "standard" exercise apparatus, the free end of the cable is attached to a circular cable wheel which is attached to a rotatable shaft supported on the main support frame. A bearing surface or surfaces, such as leg extension pads, are also attached by means of a bracket to the rotatable shaft in order that the user may apply force against the bearing surfaces to rotate the shaft and, hence, the cable wheel, against the force of gravity on the weight support members which acts against the cable. Although the resistance experienced by the user is the resistance of rotating the bearing surfaces, such resistance is constant because the cable wheel is circular and the force created by the weight support carriage provides a moment arm of constant radius which acts constantly against the cable wheel.
In an effort to provide a certain degree of variable resistance in the last-described apparatus, the cable wheel may be replaced by a cam wheel which is rotatably mounted on the shaft and which has the cable attached thereto. Thus, the torque resistance experienced by the user may have a selected maximum and minimum point which is determined by the shape of the cam wheel which serves to present differing moment arms which are acted upon by the constant force applied to the cable by the weight support carriage. However, because the resistance pattern is determined by the shape of the cam wheel, in order to present alternative resistance patterns, the cable must be detached from the cam wheel, the cam wheel removed from the shaft and replaced by a different cam wheel, and the cable attached to the replacement cam wheel. In addition to the time and effort required in changing cam wheels, to provide varying resistance patterns, a plurality of cam wheels is required.
In an effort to provide a weight lifting exercise apparatus which may provide a plurality of resistance patterns the, invention of U.S. Pat. No. 4,753,437 issued June 28, 1988 to Dr. Paul S. Lapcevic was developed. Such apparatus includes all of the components of the "standard" apparatus described hereinabove as well as a resistance converter assembly supported by the main frame and secured to the weight support carriage for varying the resistance force on the weight support carriage as the carriage is vertically moved. The resistance converter disclosed therein includes an elongated beam member having a drag weight housing, one end of which is pivotally secured to the weight support carriage, and a bearing secured by vertical members of the main frame and supporting the beam member for rectilinear movement in response to the vertical movement of the weight support carriage. As such, the vertical movement of the weight support carriage is also resisted by the weight applied to the drag weight housing so that when the beam member is in a nonvertical position, the user must also move the drag weight up an inclined plane. Because the vertical position of the bearing member is preselected, the resistance force experienced by the user may have its maximum or minimum value predetermined along the exercise movement. However, such apparatus may only provide maximum and minimum resistance forces at the beginning or end, or both, of the initial one-half of the exercise cycle, but not at other segments therebetween.
The subject invention is directed toward an improved weight lifting exercise apparatus which overcomes, among others, the problems of prior art apparatuses and which provides an exercise apparatus in which a plurality of maximum and minimum resistance force segments may be readily provided during the exercise movement.